The present invention relates to a vitamin D.sub.3 derivative, namely 1.alpha.,25,26-trihydroxycholecalciferol of the formula ##STR1##
The invention also relates to pharmaceutical preparations comprising the compound of formula I, a process for the preparation of the compound of formula I, intermediates, and a process for the preparation of said intermediates.
The compound of formula I is prepared in accordance with the invention by thermally isomerizing the compound of the formula ##STR2##
This isomerization can be carried out according to the method described in Steroids 24 (1974) 463 for the isomerization of 25,26-dihydroxyprecholecalciferol to 25,26-dihydroxycholecalciferol (e.g., in ethanol at reflux temperature).
The compound of formula II can be prepared by irradiating the compound of the formula ##STR3## according to the method described in Steroids 24 (1974) 463 for the irradiation of 3.beta.,25,26-trihydroxycholesta-5,7-diene to 25,26-dihydroxyprecholecalciferol.
The compound of formula III can be prepared by dekatalizing a compound of the formula ##STR4## wherein R.sup.1 and R.sup.2 are lower-alkyl; or R.sup.1 and R.sup.2 taken together are lower-alkylene, according to the method described in German Offenlegungsschrift No. 27 10 062 for the deketalization of 24,25-ketals.